This invention relates to the halogenation of the ring of an aromatic compound. In particular, it relates to that halogenation using a heterogeneous catalyst that is the reaction product of a support and a dopant.
Chlorinated aromatic compounds are important intermediates for making pharmaceuticals, herbicides, fungicides, and other chemicals. The chlorination of an aromatic ring requires the presence of a catalyst. Both homogeneous (single phase) catalysts, such as various metal chlorides (e.g., aluminum trichloride) and heterogenous (more than one phase) catalysts (e.g., silica, alumina, and various zeolites) have been used for this purpose. While these catalysts are effective, they are not easy to use. Homogeneous catalysts have to be kept anhydrous, more than one equivalent of the catalyst is needed for substrates that contain Lewis base sites, and it is sometimes difficult to separate the product from the catalyst. Heterogeneous catalysts, on the other hand, tend to decompose under the reaction conditions.